When to buy a new bra?

I'm about 12 weeks now. Haven't really bough maternity clothes yet, just a few drawstring pants to help me a along. I have one bra that is still fine for me. My question is, when should I go get fitted for a new bra? Is it a continuous process that your bb keep growing the entire time? I didn't know if there was a couple of different times during your pregnancy that you should go get fitted again. I had heard that around 4 weeks was a pretty standard time. Does this seem right?

I don't think there's a standard time when you should up your bra size. I invested in a couple of sports bras to get me through most of the pregnancy, and then at around 30 weeks I bought two nursing bras that I've worn throughout the past 9 weeks, and plan on wearing for nursing. I found that my breasts got bigger early on, but they haven't changed much since.